不平衡电网电压下的MMC子模块电压波动抑制方法

为降低模块化多电平换流器(MMC)对子模块电容的需求,有必要抑制子模块的电容电压波动。电网三相电压不平衡情况发生时,会加剧MMC中子模块的电容电压波动。首先分析了电网电压不平衡时MMC子模块电容电压的波动特性,进一步分析了三次谐波注入对子模块电压波动的影响;重新设计了三次谐波电压注入的幅值和相角,使其能在不平衡工况下有效实现降低电压波动的目标;设计了相应的波动抑制策略;最后,在PSCAD/EMTDC平台上进行仿真,验证了所提注入方案的有效性。

Suppression Method for Voltage Fluctuation of Sub-module in Multilevel Modular Converter with Unbalanced Power Grid Voltage

The voltage fluctuation of the sub-module in multilevel modular converter (MMC) will be aggravated with unbalanced power grid voltage. In order to reduce the MMC demand for sub-module capacitance, it is necessary to suppress the capacitor voltage fluctuation of the sub-module. Firstly, the fluctuation of capacitor voltage of MMC sub-module with unbalanced power grid voltage and the influence of third harmonic injection on sub-module voltage fluctuation are analyzed. The amplitude and the phase angle of third harmonic injection with unbalanced power grid voltage are calculated. The modulation voltage peak could be minimized by injecting the designed third harmonic voltage. The fluctuation suppression strategy is designed. Finally, the validity of the proposed strategy is verified by simulating the double-ended hybrid MMC in PSCAD/EMTDC.